Mapping attribute to create alternate keys

[ajcvickers]

Ultimately this will create a unique column (or group of columns) in the database which may or may not be used as the principal end of a relationship. In other words, it's a way to make a non-primary key column have a unique constraint without explicitly specifying a unique index.

This is not technically blocked on #4073, but should probably not be implemented until #4073 is fixed.

[firmanalams]

I'm interested in working on this issue.

[ajcvickers]

@alam157 That's great! Do you have a use-case for this? Even the fluent API here is very rarely needed.

[firmanalams]

Yes i have, so i need to create attribute [Unique] right?

[ajcvickers]

@firmanalams There is already an attribute for creating unique indexes: https://learn.microsoft.com/en-us/ef/core/modeling/indexes?tabs=data-annotations#index-uniqueness

This issue is about creating an alternate key in the EF model, which causes the model to have additional constraints over just using a unique index.